1. Field of the Invention
The present invention relates to reclosable plastic bags and packages of the type in which food products, such as chips and cereal, and other goods are packaged for sale to consumers. More particularly, the present invention relates to a reclosable zipper strip for use in transverse-zippered reclosable plastic bags made on form-fill-seal (FFS) machines.
2. Description of the Prior Art
The present invention relates to improvements in the package-making art and may be practiced in the manufacture of thermoplastic bags and packages of the kind that may be used for various consumer products, but which are particularly useful for food products which must be kept in moisture and air-tight packages, free from leakage until initially opened for access to the product contents, which packages are then reclosable by zipper means to protect any remainder of the product therein.
The prior art is fairly well-developed, but nevertheless remains susceptible to improvement contributing to increased efficiency and cost effectiveness.
In particular the present invention relates to the area of reclosable packaging known as the transverse zipper. When making a bag having a transverse zipper, the zipper is attached transverse to the longitudinal axis of the material used to make the bag, as opposed to being attached to the material parallel to the longitudinal axis. A method and apparatus for making reclosable plastic bags with a transverse zipper on a FFS machine is disclosed in U.S. Pat. No. 4,909,017.
Prior to the introduction of the transverse zipper to the reclosable packaging field, reclosable plastic bags made on FFS machines were typically made with a continuous longitudinal zipper, i.e. a zipper parallel to the longitudinal axis of the thermoplastic film used to make the bags. However, there are two primary problems with the longitudinal zipper technique. First, there is a problem in attaining satisfactory sealing of the bags against leakage since the transverse, or side, sealing bars of the FFS machine must flatten and seal the zipper at the same time they are sealing the thermoplastic film from which the packages are being made. The difficulty with which this sealing is consistently and successfully achieved is reflected by the high occurrence of leaking packages.
Second, the length of reclosable bags made on FFS machines when the zipper is attached parallel to the longitudinal axis of the thermoplastic film is limited to the diameter of the filling tube of the FFS machine. Thus, generally bags of this type are wider than they are long. While such bags are suitable for certain products where shorter bags are desirable, such as cheese and chicken parts, these bags are not suitable for applications in which longer bags are desirable, for example chips and other snack foods.
Among the approaches taken to solve these problems has been the substitution of a transverse zipper for the longitudinal zipper. When a transverse zipper is provided, the transverse sealing bars associated with the FFS machine do not flatten the zipper during formation of the top and bottom seals of the package since the transverse sealing bars may seal the zipper to the thermoplastic film transversely thereacross without having to flatten the zipper ends. In addition, when a transverse zipper is used the length of the packages made on the FFS machine can be varied while the width of the zipper remains the same.
The present invention relates to a particular type of zipper strip which may be used in transverse zipper applications, a method for attaching the zipper strip to thermoplastic film, a method for making reclosable packages on an FFS machine using the zipper strip-equipped thermoplastic film, and a reclosable package utilizing the zipper strip.
FIG. 1 depicts a cross section of a prior art reclosable plastic bag 10 made on an FFS machine having a transverse zipper strip 12 disposed at the top of the bag. The zipper strip 12 has a male profile 14 interlocked with a female profile 16. The male profile 14 has a male interlocking member 18 and a web 20 defining a trailing flange 22. The female profile 16 has a female interlocking member 24 and a web 26 defining an extended leading flange 28 and a trailing flange 30 on either side of the interlocking member.
The zipper strip 10 is initially secured to the thermoplastic film used to make the bag by sealing the extended leading flange 28 thereto. The thermoplastic film with the zipper strip thus initially sealed thereto is fed into an FFS machine where the bag is formed and the final zipper seals made by sealing the trailing flanges 22, 30 to the opposing bag walls 32, 34. The zipper strip is thus secured to the bag at three locations, denoted in FIG. 1 as seals A, B and C.
This three point seal technique, however, has proven problematic in some cases. As shown in FIG. 2, when the consumer attempts to open the bag from below the zipper by pulling outwardly on the bag walls as depicted by forces F, the female interlocking member 24 rotates and a resultant peel force S is induced at seal C. The result is that seal C is put under a relatively high peel stress, thereby weakening the seal and making detachment of the zipper strip from the bag via a peeling action likely.
It is therefore an object of the present invention to provide a zipper strip for use in transverse-zippered reclosable plastic bags which does not have the aforementioned peel problem. Another object of the present invention is to provide a method for attaching the zipper strip to thermoplastic film, which thermoplastic film can later be used on an FFS machine to make reclosable packages. Another object of the present invention is to provide a method for making packages from the zipper strip-equipped thermoplastic film. Yet another object of the present invention is to provide a package which utilizes the zipper strip.